I was looking over messages that came in while my wife and I were
vacationing during the holidays, and I noticed the question about
batteries did not seem to gather many responses. So I offer the
following in hopes of being helpful.
The ordinary 1.5 volt energy cell has a carbon rod at its center which
is the cell's anode. The cell's cathode is a cylindrical cup of zinc
metal, the outer case of the cell. The space between the anode and
cathode is filled with a paste of manganese dioxide, ammonium chloride
and water. (see primitive graphic):
When the cell is in use, electrons leave the cathode and re-enter the
anode. The energy is provided by zinc metal reacting with the ammonium
chloride to form zinc chloride. The free ammonium ions react with
manganese dioxide at the anode to form manganese (III) oxide and ammonia
and water and ammonium hydroxide. The reactions proceed slowly but
inevitably even when the cell isn't being used.
Note that the zinc metal outer case is "dissolved" by the reaction, and
that the case is doomed to become thinner and thinner until eventually
it gets eaten all the way through in places. The wet paste of chemicals
is then free to leak through the holes in the zinc.
Energy cells are almost always installed in series, so leaving the cells
in equipment doesn't usually cause more leakage; but it allows the wet
slightly acidic chloride leakage to do a lot of damage to the equipment.
If leaking cells are left out in the open, the water evaporates almost
immediately and the leakage is much less evident and less messy. The grey
powder you mention seeing is dried zinc chloride.
The C-Zn cell is pretty ancient technology, 99% guaranteed to develop
leakage at some point in its life, a relic that lives on mainly because of
its low cost. IMHO one should use only alkaline energy cells or
rechargeables in electronic equipment. Leakage in the newer types of
cells is not impossible but pretty unlikely. Use C-Zn cells only in
equipment you are willing to see destroyed by chemical leakage.
You can see the reason for the leakage by cutting open an old C-Zn
energy cell and viewing what the reaction has done to the zinc metal
case. DO NOT TRY TO OPEN ANY OTHER TYPE OF ENERGY CELL!!! People have
sustained injuries trying to open alkaline cells, Hg cells, etc.
Best wishes,
Larry
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright
Physics, Physical Science, Internet Teacher
Charlotte High School, 378 State Street, Charlotte MI 48813
<physics@scnc.cps.k12.mi.us> or <science@scnc.cps.k12.mi.us>
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*** ORIGINAL MESSAGE ***
Date: Mon, 21 Dec 1998 20:08:47 -0500
From: Yvon Jean <phys@NTL.SYMPATICO.CA>
Subject: battery leakage
Can anyone explain to me why there is battery leakage after a prolong
storage of an ordinary 1.5 V battery. By leakage I mean the greyish
white powder that forms around the battery near the top (or bottom?).
Is there more chance of leakage if the battery is left in the electronic
equipment (Walkman, etc...)?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
from Larry Cartwright
Physics, Physical Science, Internet Teacher
Charlotte High School, 378 State Street, Charlotte MI 48813
<physics@scnc.cps.k12.mi.us> or <science@scnc.cps.k12.mi.us>